Why aren't my new earbuds working with Cortana on my Lumia 930?

I have purchased Sennheiser cx275s earbuds to use with my Lumia 930, sound is excellent but cortana does not pick up the Hey Cortana or read my txt messages anymore. I have looked through the settings but I may have missed a setting to reset ? Just not sure any thoughts appreciated or a recommendation of a good quality set that will work fully ?